I have seen some people wearing red threads or
strings around their wrist and even necks. Is there any source
for this, or is it "superstition?" Thanks..

Aytan Ben-Pelech from Australia wrote:

Dear Rabbi,

Recently I was in Jerusalem and when I visited the
Kotel I was approached by a woman who tied a red string around
my hand and said a blessing. I have asked numerous people for
an explanation and I have received just as many different answers.
Perhaps you can help.

Name Withheld wrote:

Dear Rabbi,

Could you please explain to me the history of
the red bendel. I received one recently from a friend that had
traveled to the Wall. What does it mean when the bendel falls
off your wrist?

Dear Moshe, Aytan Ben-Pelech and Name Withheld,

One of the items necessary for the building of the
Holy Sanctuary was red thread. The dye for the red thread came
from a type of worm. Rabbi S. R. Hirsch points out that the worm
was the lowliest form of life, and yet it was intrinsic to the
building of the Sanctuary.

The red string is thought by some to ward off the
"evil eye." Rabbi Eliyahu Dessler explains the "evil
eye" as follows: If a person is blessed with good fortune
and he becomes haughty as a result, this might arouse jealousy
in others. In this sense, his good fortune is negative. This
calls his good fortune into question and may cause him to be re-judged
in Heaven.

The red thread, reminiscent of the lowly worm, can
be seen as protection against this. Each time a person looks
at the string he is reminded that a person is really as lowly
as a worm. This humility is the ultimate weapon against the "evil
eye."

Having said that, many great Rabbis frown upon it.

What does it mean when it falls off the wrist? It
is an extremely significant sign: It signifies that it was not
tied on properly.